Process for making paper pulp



' Patented Sept. 27,1927.

fUNlTED STATES 1,643,826 PATENT OFFICE.

BEBTBAND 8. SUMIEBS, GI PORT HURON, MICHIGAN.

PROCESS FOR IAKING PAPER PULP.

30 Drawing.

The invention which forms the subject matter of the present specification relates to the so-called sulphite process for digesting vegetable fibers to make paper pulp, in

5 which the digesting liquor contains sulphites such as those of calcium or magnesium with a considerable excess of sulfurous acid. Such a process is set forth in Patent No. 1,584,902 granted to me'May 18th, 1926.

19 The digesting agent in this process attacks and weakens the fiber treated in many cases and particularly where the fiber is more susceptible to attack as in the case of flax vwhich contains both pecto and ligno celluloses. Not only is a weaker pulp produced than if the full-strength of the fiber were retained but the yield in pulp is less than it otherwise would be.

I have discovered that by the addition of 29 a small amount of phosphoric acid H to the liquor itis possible to more or less protect" the fiber from the action of the digesting agent, particularly in the case of the moresusceptible fibers such as those of the flax 5 plant. The addition of phosphoric. acid minimizes the devastating action of the liquor on the bast or pecto cellulose fibers,

which are more readily attacked than the v ligno cellulose fibers, while the latter are 30 being reduced tothe condition of pulp. The presence of the phosphoric acid in the cook has a hardening effect on the pulp and therefore the proportion of this reagent used is determined with reference to the nature of the pulp-desired and the particular character of the vegetable fiber being treated.

In practicing my process the procedure need not vary from that commonly employed in the sulphite process except for the introduction of the phosphoric acid. The proportion of the latter introduced may vary within wide limits and it may be in-' troduced in a variety of forms, it only being essential that it remain in solution when added to the cockpit is essential, however. that the phosphoric acid in the presence of the sulfurous acids and its compounds in the cook remain soluble and do not seriously affect the reagents of the cook.

I prefer to use the phosphoric acid in the form of trisodic phosphate and ordinarily employ 1 to 4% thereof, though it may be used in greater or smaller amounts without departing fromthe invention and with ben- -eficial results, depending upon the. nature of the vegetable material to be pulped and Application filed December 22, 1928 Serial No. 882,309.

the character of the pulp desired, the hardness of the pulp depending largely upon the amount of phosphoric acid used. Other soluble phosphates may be used, for exam ple, the neutral or acid phosphates of soda and the other alkali metals but I prefer trisodic phosphate as it is readily obtained on the market and I find that when alkaline salts are used there is less tendency for the cook to burn. It will be evident to those skilled in the art that where a reagent containinga greater proportion of phosphoric acid is used the proportion thereof should be correspondingly changed.

It will be evident that where trisodic phosphate is added to a liquor containing considerable quantities of free sulphurous acid a certain amount of free phosphoric acid is liberated, the sodium of the phosphate combining with sulfurous acid. It is important that the sulfurous acid remain in suflicient excess during the cook as compared with the base to prevent the deposition of calcium or other base, the precipitation of which would be aptto result in a burnt cook. For a similar reason the alkaline phosphate is superior to the alkaline earth phosphates. The latter may be used, however, where the sulfurous acid in the cook' is in sulficient excess.

- The phosphate is preferably added to the cooking liquor, which may be otherwise prepared in the usual way, before the liquor is introduced into the digester though quite satisfactory results may be obtained by dumping the phosphate into the digester and'running the sulphite liquor onto it.

As a matter of economy after the completion of a cook the liquor, instead of being led to the sewer as inv the usual practice, maybe passed through-quick or slack lime and then either allowed to settle or filter whereby the phosphates in solution unite with calcium of the quick lime forming in-- soluble phosphates from which alkaline phosphates maybe regenerated by. the use of sulfuric acid and alkalies in an obvious manner. This method of regeneration is particularly desirable where the amounts of phosphates used are large. I

I claim:

1. An acid process'for digesting vegetable fiber which consists in treating the fiber with an acid digesting liquor containing phosphoric acid.

2. A process of pulping vegetable fiber which consists in digesting the same with bi-sulfite liquor containing phosphoric acid.

3. A process for pulping vegetable fiber consisting in digesting the same with bisulfite liquor and a phosphoric acid salt of an alkali metal.

4. A process of pulping vegetable fiber which consists in digesting the same with bi-s'ulfite liquor containing phosphoric acid in the form of a salt capable of mixing with said liquor without precipitation.

5. A process for pulplngvegetable fiber -which consists in digesting it in a liquor consaining trisodic phosphate and sulfurous aci 6, A process for pulping vegetable fiber which consists in digesting it in a liquor containing a sulphite and a soluble compound of phosphoric acid.

7. A process for pulping vegetable fiber which consists in digesting it in a digesting liguor containing phosphoric acid, drainin o the-liquor from the pulped material an reclaiming the hosphoric acid.

8. A process or making aper pulp which consistsin digesting it in a iquor containing a; digesting agent and phosphoric aci bringing the spent liquor into intimate con tact with lime, separating the precipitated phosphate of lime from the liquor and recovering phosphoric acid therefrom.

9. A liquor for which contains, 5111 urous acid and phosphoric acid. I

10. A liquor for pulping vegetable fiber containing a bi-sulfite, sulfurous acidand phosphorous acid.

11. A liquor for pulpin vegetable fiber containing a bi-sulfite, sul rous acid, and

a soluble phosphate.

BERTRAND s. SUMMERS.

ulping vegetable fiber 

